Tiny Generator Uses Heat to Power Wearables

An innovative solution from a team at the Korean Institute of Science and Technology could hold the key to powering wearables continuously, using the wearer's own body heat as a generator.

Unlike most people today, I still wear a wristwatch. I bought it six years ago in Japan, and the great thing about my Citizen Eco-Drive is that I've never had to change the battery: It runs on a solar-powered rechargeable battery.

We're all used to plugging in our devices overnight, and sometimes during the day, to make sure they have sufficient power. But sometimes we forget, and suddenly our beloved gizmos die when needed most.

Now, with a new wave of wearable technology arriving like a whirlwind, we're facing more technology that needs frequent charging. Although most smartwatches and fitness bands popping up in the market today do not require daily charging, eventually we'll forget to plug them in, and they'll run out of juice.

An innovative solution from a team at the Korean Institute of Science and Technology could hold the key to powering wearables continuously, using the wearer's own body heat as a generator. The Korean team, led by Byung Jin Cho, has designed a new light and flexible generator made out of thermoelectric (TE) substances printed on glass fabric.

The output power per unit weight is remarkable (28 mW/g at 50 K) and could be used to provide enough energy to charge a smartwatch.

For example, the Sony SmartWatch 2 promises three days to one week battery power depending on use, but in reality, to be fully functional it needs to be charged every other day. The watch uses a Li-polymer 140 mAh battery. If you installed a slim TE strip on the SmartWatch wristband, it could power the watch and enable it to function without the user worrying about the battery dying.

The concept isn't new. For years researchers have been looking at ways to harvest body heat and produce electricity, but the size and weight of the devices, and the limited amount of power collected this way, made the technology ineffective for commercial use -- until now.

What's new about the Korean design is its use of a "glass fabric-based textile," which is made by screen printing on inorganic materials, and its use of a self-sustaining structure of a TE device without top and bottom. According to the paper, the developed device not only achieves unprecedentedly large output power density but also "can be bent as low as 20 mm without change in performance upon repeated bending for up to 120 cycles." The team concludes: "The output power per unit weight is remarkable (28 mW g-1 at a ΔT = 50 K), and this will facilitate its use in applications where the weight of the TE device is critical."

If further tests are successful, we should start seeing wearable devices, such as the Sony SmartWatch or Samsung's Gear, without the need of external charging early next year.

— Pablo Valerio is a freelance blogger who writes about mobile and telecom issues for EE Times. He lives and works in Barcelona.

Wonder what sort of regulation this little guy needs before it's useful to be plugged in. I don't particlarly imagine watchmakers jumping at the prospect of adding a regulator IC on the already small footprint.

Hello, does not work in temperate climates where the temp difference is small and heat transfer away from the 'generator' is not a sure thing. And as a Norwegian I know it's not going to work in winter. I'm not going to bare my wrists! Thus the temperature inside my jacket and mittens cafrefully covering my wrists is the same as my external body temperature ie no energy can be harvested. A lot more work is needed.

However, if someone comes up wirt a safe and efficient way to move energy from the shoes to the wrist (apart from wires or using the body's blood stream) then we start talking re how to power a werable device!

Assuming 15C delta temp(pretty high for typical users) and 140mAh battery that lasts a day I calculate it would take roughly 46 cm2 to power it. That is about one order of magnitude too large for typical wearables. It is nice work but 46 cm2 worth of solar cell will also power this in an office environment. If you get an athlete in a cold environment the numbers do start to look reasonable.